calling conventions for MIPS 2000/3000

Can someone provide me a cogent description of the C calling
conventions for the MIPS 2000/3000? I'm executing on DECstations and
DECsystems running Ultrix 4.x and using cc.


I have read Kane (particularly the section "Linkage Conventions" in
Appendix D), but don't think that all the details are spelled out.


In particular I am confused about the size of the "procedure call
argument area". I realize that I must allocate space here even though
arguments are being passed in registers. What I'm baffled about is
exactly how much space must be allocated here.


For example, for this simple C function,


void main()
{
                 float x;


                 x = 1.0;
                 printf("%e\n",x);
}


"cc -O" generates a frame of length 24 bytes. This apparently
includes 4 unused bytes at the "top" of the frame, 4 bytes for saving
r31, and 16 bytes for the arguments area. Why 16 bytes here? It looks
like only 12 bytes are needed, 4 for the char * first parameter and 8
for x converted to a double. But if only 12 bytes are allocated then
printf prints garbage.


Phil Hatcher
Dept. of Computer Science
Univ. of New Hampshire
Kingsbury Hall
Durham, NH 03824
603-862-2678
pjh@cs.unh.edu
--

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